Conventionally, speech dialog interfaces have been developed as interfaces between robots or machines such as car navigation systems and human users. Machines having dialog interfaces interact with users through dialogs with the users and machines' actions performed based on information obtained from the dialogs.
For example, Japanese Patent Application Publication No. 2003-316385 discloses the following technique. In order to allow free interaction between a user and a machine, a task (domain) corresponding to a speech recognition result of a user's utterance is selected from a plurality of tasks to automatically generate a sequence of dialogs. When the user further utters, a transition takes place to a sequence of dialogs of a corresponding task as necessary, and then the sequence returns to the original sequence.